The alignment of satellite galaxies in gasdynamic simulations

点击翻译按钮获取中文摘要

The confinement of satellites to the polar regions of galaxies has confounded astronomers for at least 40 years. Neither the observations of this effect in external galaxies (first seen by Holmberg 1969) nor in our own Milky Way have been adequately explained in the intervening four decades. In fact, more recent observations of the alignment of satellite galaxies in large scale surveys such as the SDSS and in the 2dFGRS have contradicted the so-called Holmberg effect and found that satellites tend to align themselves with the plane of their host galaxies. Regardless of what the sense of the anisotropic distribution is, that satellites are not uniformly distributed within their parent halos has caused a number of authors to highlight that this is in disagreement with the simple predictions of the standard concordance cosmology. Until now, theoretical descriptions have tried to reconcile the isotropic distributions of satellites found in simulations with the observations. Many authors have employed dark matter only simulations in a bid to study the alignment of satellites in the local group. Although some progress has been made in understanding why satellites are anisotropically distributed, the sense of their flattening with respect to the central galaxy has all but evaded analysis. The reason for this is simple: running hydrodynamic simulations in a large cosmological volume is expensive and is necessary for determining the orientation of a central galactic disc. By using one of the largest hydrodynamical simulation ever run we wish to address a 40 year old unsolved mystery: is the Milky Way a gross exception with its polar alignment? or is its flattening typical of similar galaxies.